ABI: sysfs-devices-power: add some debug sysfs files

Those files were added back in Apr 2010, but there's no
documentation for them yet.

Fixes: c92445fa ("PM / Runtime: Add sysfs debug files")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/df6c3ae0ffc2dddf73d7a5baf696a4aa260fb576.1632750608.git.mchehab+huawei@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-devices-power

@@ -283,3 +283,25 @@ Contact:	Arjan van de Ven <arjan@linux.intel.com>
 Description:
 		Reports total time that the device has been suspended.
 		Used for runtime PM statistics.
+
+What:		/sys/devices/.../power/runtime_usage
+Date:		Apr 2010
+Contact:	Dominik Brodowski <linux@dominikbrodowski.net>
+Description:
+		Reports the runtime PM usage count of a device.
+
+What:		/sys/devices/.../power/runtime_enabled
+Date:		Apr 2010
+Contact:	Dominik Brodowski <linux@dominikbrodowski.net>
+Description:
+		Is runtime PM enabled for this device?
+		States are "enabled", "disabled", "forbidden" or a
+		combination of the latter two.
+
+What:		/sys/devices/.../power/runtime_active_kids
+Date:		Apr 2010
+Contact:	Dominik Brodowski <linux@dominikbrodowski.net>
+Description:
+		Reports the runtime PM children usage count of a device, or
+		0 if the the children will be ignored.
+